I been reading WWI submarine warfare this summer. I had sketchy knowledge on the subject. I did find some good general history , but now I'm looking for more first person accounts.
"The Journal of Submarine Commander von Forstner" by Georg-Gunther von Forstner. in public domain
https://uboat.net/wwi/men/commanders/76.html
"To the Last Salute: Memories: of an Austrian U-boat Commander" by Georg von Trapp. This was a surprise. I found this a fascinating personal narrative of the Adriatic / Mediterranean front, and his everyday experiences and tactics on early Austrian U-boats.